FIG. 14 shows a schematic view of one example of a conventional polarization plate 50 to be used for a liquid crystal panel. The polarization plate 50 is a multi-layered plate on which a polarizer 51 and a pair of transparent polarizer protective films 52a and 52b are laminated with adhesive layers 53a and 53b. A film stretched in one direction after containing a dichromatic dye, such as an iodine complex or the like in a polyvinyl alcohol (PVA)-based film is used as the polarizer 51. Stretching the film in one direction enables the dichromatic dye to be oriented in a stretching direction together with polyvinyl alcohol molecules, which leads to have polarization functions. However, the mechanical strength of the polyvinyl alcohol-based film itself is low. Thus, the stretched polyvinyl alcohol-based film can easily shrink and is apt to be deformed under humidified conditions wherein moisture in air is absorbed. Accordingly, it is difficult to use the polarizer 51 alone as a polarization plate.
Therefore, the polarizer protective films 52a and 52b are bonded to both sides of the polarizer 51 with the adhesive layers 53a and 53b to reinforce the mechanical strength and humidity resistance so as to be used as the polarization plate 50. The polarizer protective films 52a and 52b made of transparent triacetyl cellulose (TAC) based-resin have been widely used. The adhesive layers 53a and 53b wherein a cross linking agent is being mixed with a polyvinyl alcohol aqueous solution have been widely used. The polarizer 51 has a thickness of about 60 μm, the polarizer protective films 52a and 52b respectively have a thickness of about 80 μm and the adhesive layers 53a and 53b respectively have a thickness of about 100 nm.
The typical configuration of the conventional polarization plate 50 comprises: the polarizer protective film 52a made of transparent triacetyl cellulose-based resin (thickness: 80 μm)/the adhesive layer 53a made of polyvinyl alcohol-based resin (thickness 100 μm)/the polarizer 51 (thickness: 60 μm)/the adhesive layer 53b made of polyvinyl alcohol-based resin (thickness: 100 μm)/the polarizer protective film 52b made of transparent triacetyl cellulose-based resin (thickness: 80 μm).
The material of a polarization plate is generally made longer than a liquid crystal panel. A rectangular-shaped polarization plate in the size of a liquid crystal panel is cut out from such an elongated polarization plate material. For instance, in the case of the conventional polarization plate 50, the polarization plate 50 in the size of a liquid crystal panel has been cut out from the material of the polarization plate using a cutter for punching.
However, when cutting out is carried out using a cutter for punching, threadlike film fracture pieces may be produced on an end face of the cut away polarization plate 50. Such threadlike fracture pieces need to be removed because such fracture pieces cause deterioration in quality.
Conventionally, the threadlike fracture pieces of the end face of the polarization plate 50 have been cut with a rotating knife (Japanese Patent Publication No. 2004-16763 A). Fullback machining with a milling machine is suitable for removing and machining the threadlike fracture pieces with the rotating knife. When the end face of the polarization plate 50 is practically cut by fullback machining, it is efficient to work end faces of a plurality of polarization plates 50 all together, where the plurality of polarization plates 50 in the size of a liquid crystal panel are laminated on each other to make the total thickness from 10 to 100 mm and make the machining allowance from 0.5 to 10 mm. One example of appropriate conditions of fullback machining is: spindle rotation rate: 4,500 rpm and work feed rate: 800 mm/minute. The machining precision and machining efficiency are both good in such conditions. It is suitable to decrease the total thickness when the machining allowance is large and increase the total thickness when the machining allowance is small.
The fullback machining mentioned above removes the threadlike fracture pieces of the end faces of the polarization plates 50 to prevent the liquid crystal panel from being deteriorated in quality caused by the threadlike fracture pieces.